Silicon carbide structures



A ril 28, 1970 R. c. WHITE ETAL SILICON CARBIDE STRUCTURES Filed 5, 1967 co m 0 v cu I u o INVENTORS RUDOLPH C. WHITE '7 HAROLD R. DAWS ATTORNEYfi United States Patent 3,508,954 SILICON CARBIDE STRUCTURES Rudolph C. White, Midlothian, and Harold R. Davis,

Richmond, Va., assignors, by mesne assignments, to Texaco Inc., New York, N.Y., a corporation of Delaware Filed Oct. 5, 1967, Ser. No. 673,054

Int. Cl. C23c 11/00 US. Cl. 117106 3 Claims ABSTRACT OF THE DISCLOSURE Silicon carbide structures are made by heating a refractory substrate to a temperature of from about 2100" F. to about 2500 F. in an atmosphere of methyltrichlorosilane, methyldichlorosilane and hydrogen. The method is particularly useful for the production of filaments of high tensile strength and high elastic modulus.

The invention relates to a method of producing silicon carbide filaments and other structures combining a high tensile strength and high elastic modulus with hardness and resistance to oxidation.

We have found that structures having useful combinations of the desired physical and chemical properties can be produced by depositing a layer of silicon carbide on a refractory substrate by heating the substrate to a temperature of from about 2100 to about 2500 F. in an atmosphere containing methyldichlorosilane and methyltrichlorosilane in the proportion of from about 1 to 3 to about 1 to by volume and from about 50% to about 80% by volume of hydrogen.

The method of the invention is particularly suitable for the production at high rates of deposition of oxidation resistant filaments having high tensile strength of the order of 400x10 p.s.i. and modulus values upwards of 60x10 p.s.i. which are useful in the production of composite structural members having various applications such as high strength lightweight airfoils, by incorporating the filaments in a plastic, elastic, vitreous, cementitious or metallic matrix Particularly useful as substrates for the silicon carbide structures are filaments of conductive refractory substances such as tungsten, rhenium, tantalum, titanium, molybdenum, iron, copper, nickel and nichrome.

An illustrative example of the method of the invention will be described with reference to the accompanying drawing which is a diagrammatic representation of apparatus useful in practising the invention.

The apparatus shown in the drawing comprises a preheating chamber generally designated 10 and a silicon carbide deposition chamber generally designated 11. A substrate filament 12 is passed continuously at a substantially uniform rate of travel from power-driven feed spool 13 successively through the preheating chamber and the silicon carbide deposition chamber to power-driven takeup spool 14. The preheating chamber and the deposition chamber are sealed from each other and from the surrounding atmosphere by means of Y-shaped mercury seals 15 connected by flexible tubes 24 to separate level adjusting reservoirs 16. The mercury seals also serve as contactors for the supply of heating current to the substrate filament in the preheating and deposition chambers. Tension on the substrate filament is maintained substantially constant by suspending a tensioning weight 26 in a loop of the filament. Ts 17 and associated T-connectors 18 serve as inlets and outlets for gases into and out of the preheating and deposition chambers and also for the support of adjustable guide loops 19 for the substrate filament.

3,508,954 Patented Apr. 28, 1970 Hydrogen or other purging gas may be supplied to preheating chamber 10 through tube 20 and removed through tube 21 for the purpose of removing absorbed, adsorbed or reacted oxygen from the surface of the substrate filament as it passes through chamber 10. Lubricants or other surface impurities are also removed from the filament by evaporation or by reaction with the hydrogen.

Heat-jacketed vessels 25 provide means for vaporizing the methylhalogensilanes and causing the vapor to flow through suitable metering devices 28 into a mixing chamber 29 into which hydrogen may be introduced through pipe 30. The mixture of hydrogen and methylhalogensilanes is supplied to chamber 11 through tube 22 and residual gases and vapors pass out of chamber 11 through tube 23 to recovery or disposal means (not shown).

Glass is a suitable material of construction for the preheating and deposition chambers and for the connections thereto and therebetween. The flexible tubing can be made of polyethylene and the T-connectors 18 can be of copper.

Instead of introducing the methylhalogensilane and hydrogen mixture into one end of chamber 11, the mixture may be introduced at the middle of the chamber and the residual gases and vapor removed at the two ends or the mixture may be introduced at the two ends and the residual gases and vapors removed at the middle of the chamber. Also, instead of using a single silicon carbide deposition chamber, the deposition may be carried out in a plurality of serially connected chambers under the same or different operating conditions.

The following is a representative example of the operation of the method of the invention:

A 0.5 mil tungsten wire is passed through the apparatus at a speed of about 5 feet per minute. It is heated to about 2200 F. in a current of hydrogen in the preheating chamber 10. In the five foot silicon carbide deposition chamber 11 it is heated to about 2300" F. A mixture of 30% by volume of methyltrichlorosilane and 5% by volume of methyldichlorosilane in hydrogen is supplied to the chamber resulting in the deposition of silicon carbide to an overall filament diameter of about 4 mils.

We claim:

1. A method of making silicon carbide structures which comprises heating a refractory substrate to a temperature of from about 2100 to about 2500 F. in an atmosphere containing methyldichlorosilane and methyltrichlorosilane in the proportion of from about 1 to} to about 1 to 10 by volume and from about 50% to about by volume of hydrogen.

2. A method of making silicon carbide filaments which comprises passing a refractory filament through an atmosphere containing methyldichlorosilane and methyltrichlorosilane in the proportion of from about 1 to 3 to about 1 to 10 by volume and from about 50% to about 80% by volume of hydrogen while heating the refractory filament to a temperature from about 2100 to about 2500 F.

3. A method as defined in claim 2 wherein the refractory filament is tungsten.

References Cited UNITED STATES PATENTS 3,157,541 11/1964 Heywang et al.

FOREIGN PATENTS 145,106 1962 U.S.S.R.

ANDREW G. GOLIAN, Primary Examiner US. Cl. X.R. 23208 

